1. Field of the Invention
The present invention relates generally to the treatment of molten copper metal, and specifically to apparatus for and a method of continuously filtering and optionally degassing molten copper and otherwise extracting impurities therefrom.
2. Description of the Prior Art
U.S. Pat. Nos. 2,429,584, 3,537,987, 3,610,600, 3,820,767, 3,904,180, 3,972,709, 4,067,731, and references therein are among numerous patents illustrating that filtering and degassing of molten metal are generally well known in the prior art. Applicants believe that until the present invention, there has been no effective system for continuously removing solid and gaseous impurities and contaminants from molten copper.
The majority of molten metal filtering and degassing technology has focused on aluminum in part because purity is particularly critical in aluminum and because the relatively low melting temperature of aluminum makes it much easier to treat than most metals. Molten aluminum treatment has progressed from batch-type slag filtering and fluxing, through in-line granular and woven refractory filtering and fluxing, to the in-line use of disposable porous ceramic foam filters such as those disclosed in U.S. Pat. Nos. 4,007,923, 3,917,242, 3,893,917, 3,962,081 and 4,092,153. Other metals, including cast iron and steel, are often degassed by a vacuum using reactive ingredient methods, while molten copper treatment technology has been limited to few improvements one being the use of catalytic action to deoxidize a melt.
Three major grades of copper recognized in the molten copper treatment industry are tough pitch copper, fire-refined copper and electrolytic copper. As used herein these terms are given what is believed to be their usual and common meanings in the industry as defined in Volume 1 of Metals Handbook, Eighth Edition published in 1961 by the American Society for Metals. Tough pitch copper is: "Copper containing from 0.02 to 0.05% oxygen, obtained by refining copper in a reverberatory furnace." Electrolytic copper is: "Copper which has been refined by electrolytic deposition, including cathodes which are the direct product of the refining operation, refinery shapes cast from melted cathodes, and by extension, fabricators' products made therefrom. Usually when this term is used alone, it refers to electrolytic tough pitch copper without elements other than oxygen being present in significant amounts." Fire-refined copper is: "Copper which has been refined by the use of a furnace process only, including refinery shapes and, by extension, fabricators' products made therefrom. Usually, when this term is used alone it refers to fire-refined tough pitch copper without elements other than oxygen being present in significant amounts."
Applicants believe that there is no known prior art method for continuously filtering or cleaning molten copper and for this reason, most manufacturers of cast copper products rely solely on the inherent purity of electrolytically refined copper for production of high quality castings. For molten copper known to be contaminated by refractories or the like, the only present alternative to accepting a poor quality product is scrapping the product for remelting. One example of contamination is where steel strapping normally used to bundle cathodes for shipment is inadvertently charged into a melting furnace along with the cathodes despite the normal precautions. Since our invention filters and extracts contaminants and impurities from copper, particularly, iron and calcium, by adsorption, use of the present invention immediately prior to casting negates duplication of refining effort, thereby a higher percentage of superior quality cast products can be produced from a typical melt at less overall cost. One of the main manufacturing processes which traditionally relies on the inherent purity of electrolytically refined copper is that of continuous casting and rolling of copper into rod wherein molten copper is cast into a continuously advancing mold cavity formed by at least one endless moving mold surface in conjunction with other mold surfaces so as to form a closed mold cavity. The molten copper is solidified in the shape of said mold cavity to form a cast bar which is then extracted for further processing such as rolling into copper rod suitable for drawing into wire.
It is a generally accepted principle of the casting arts that the quality of a cast product is more related to the particle size of inclusions in the matrix than to the number of inclusions and this is particularly true when the casting is intended for reduction into wire rod which will ultimately be drawn into wire for use in electrical conductor, magnet wire or telephone wire. When copper rod containing an inclusion is drawn to a point fine enough that the inclusion's diameter becomes significant with respect to the diameter of the wire a reduction in effective cross-sectional area is produced. Those in the art assume that a wire break will occur when the inclusion diameter "d" becomes an appreciable fraction of the "downstream" wire diameter. It is also generally assumed in the wire making industry that there exists a critical inclusion size "d.sub.c " for a given "downstream" wire diameter and that the condition for a break is: d.gtoreq.d.sub.c. Thus it is apparent that there is a need for apparatus for and a method of controlling the diameter of inclusions cast into the matrix of copper castings intended for use in the copper wire industry. A detailed analysis of this problem of the wire industry is found in "Wire Breaks In Copper: A Classification and Analysis"; Chia et al; Wire Journal, February, 1976.
Fire refined copper often contains many metallic and nonmetallic impurities which are detrimental to finished products such as wire made directly from fire refined copper. When fire refined copper is cast into anodes for electrolytic refining, these impurities result in heavy accumulations of waste sludge in the electrolytic reservoirs or cells. Use of the present invention as a filter for molten fire refined copper improves its quality, thereby making it acceptable for some applications without additional refining, and reduces impurities in cast anodes destined for electrolytic refining.
Another problem often occurring in the prior art is clogging of the tundish spout. The ceramic spout disclosed in U.S. Pat. No. 3,752,372 is representative of the type of spouts used to cast molten copper. Molten copper will not wet or stick to a spout of this type; however, certain impurities and contaminants such as iron will deposit on the surface of the spout, which in turn results in casting difficulties which take the form of a clogged spout which often interrupts the molten metal flow. By lowering the amount of these impurities and contaminants from the melt through the application of our invention, this problem is substantially reduced.